1. Field of the Invention
The present invention relates to an acceleration control device for a motor vehicle and, more particularly, to a signal processing system for correcting the output voltage of a sensor which is associated with an accelerator such as an accelerator pedal of the motor vehicle for outputting depression of the accelerator pedal in terms of changes in the resistance thereof.
2. Description of the Related Art
In recent years, introduction of electronic techniques into control of a motor vehicle has progressed so far that a variety of mechanically controlled parts are being replaced by electronically controlled ones. In order to use this type of electronic control, displacements or the like of the respective parts have to be converted into electric signals so that sensors can be used with those parts. Of these, for example, an acceleration sensor is used with the accelerator pedal so as to detect a driver's actuation or depression of the pedal. The output signal of the acceleration sensor will be termed herein as "an acceleration signal", and is used to control the throttle of an internal combustion engine, a clutch attached thereto along with timing of a speed change for an automatic transmission and so forth. Thus, the acceleration signal is used for most of the controls of the drive power train of the vehicle so that its accuracy has a direct effect on and important relationship with the performance of the engine.
In the acceleration control device of the prior art, however, the acceleration signal has such nonlinear characteristics with respect the angle of the sensor when using a potentiometer, i.e., during the depression of the accelerator pedal. In other words, the sensor fails to have an angle of deflection which is in a linear relationship with the output voltage thereof.
Since the sensors are mass-produced and have their resistances dispersed over a range, moreover, the above-mentioned engine control signal characteristics require that the output voltages of the sensors be set at a zero point when the accelerator pedal is released or not depressed. As a result, the nonlinear characteristics among sensors are dispersed over a range.
The quantities to be controlled thus fail to change linearly with the depression of the accelerator pedal by the driver. As a result, the relationship of the pedal depression with the throttle opening of the engine and the speed change timing of the transmission are changed to produce a disadvantage in that the drivability or driving feeling of the vehicle is degraded. Since these characteristics are different between the respective vehicles, the drivability or driving feeling becomes even worse. At the same time, the output voltages during idling and at the maximum depression of the accelerator pedal are different among the sensors thereby causing another disadvantage in that an insensitive range is caused at the depression side thereby enlarging the range of dispersion. This results in the respective vehicles being different in the throttle opening and/or the speed change timing for a pedal depression which is the same thereby causing still another disadvantage in that the vehicles do not produce a common performance.
In order to eliminate the above disadvantages, it is a current practice to extract the signal of the sensor from three terminals, i.e., two terminals of a fixed resistance and one terminal of a sliding contact so that the potential of the sliding contact may be outputted as a divided voltage between the two terminals of the fixed resistance. However, this current practice has a further disadvantage in that the wiring is accordingly complicated and raises the production cost.